Enhancing the stability and efficiency of the anammox process in plug-flow integrated fixed-film activated sludge (IFAS) reactors through alternating anoxic/aerobic (A3) conditions

Abstract

The breakthrough of this study was the development of plug-flow integrated fixed-film activated sludge (IFAS) reactors operated with alternating anoxic/aerobic (A³) conditions for enhanced anammox processes. The energy-saving capacity and efficiency of this A³-IFAS system was compared with an identical IFAS reactor operated with continuous low oxygen aeration (CLOA) through a test period of 141 days. At the nitritation start-up phase, the nitrite in the effluent of the A³-IFAS system quickly accumulated to 77.9%, which was higher than that of the CLOA-IFAS system (61.7%). The A³-IFAS system reached 94.1 ± 4.0% of total inorganic nitrogen (TIN) removal in the stabilization stage, which was higher than that in the CLOA-IFAS system (66.7 ± 5.3%). A³-IFAS maintained stable partial nitrification and TIN removal, whereas the nitritation in CLOA-IFAS was disturbed on the 96th day and the TIN removal became unstable. Quantitative real-time polymerase chain reaction (qPCR) analysis indicated that ammonia-oxidizing bacteria (AOB) were dominant in both IFAS reactors, while the amount of nitrite-oxidizing bacteria (NOB) in the CLOA-IFAS system was 5.27 times that in the A³-IFAS system. The kinetic analysis revealed that the ratio of the AOB specific growth rate (μ^AOB) and NOB specific growth rate (μ^NOB) in A³-IFAS was 4.09, which was higher than that (3.1) in the CLOA-IFAS system, implying that the low growth rate of NOB in anoxic zones is the main reason for the stable nitritation and high TN removal in A³-IFAS.